Proximity-Induced Gap Opening by Twisted Plumbene in Epitaxial Graphene.

Besides graphene, further honeycomb 2D structures were successfully synthesized on various surfaces. However, almost flat plumbene hosting topologically protected edge states could not yet be realized. In this Letter, we investigated the intercalation of Pb on buffer layers on SiC(0001). Thereby, suspended and charge neutral graphene emerged, and the intercalated Pb formed plumbene honeycomb lattices, which are rotated by ±7.5° with respect to graphene. Along with this twist, a proximity-induced modulation of the hopping parameter in graphene opens a band gap of around 30 meV at the Fermi energy, giving rise to a metal-insulator transition. Moreover, the edges of the intercalated plumbene layers revealed edge states within the gap of the conduction bands at around 1 eV as expected for charge neutral plumbene.